Expansion of g/(1 - x^4*g^2), where g = 1+x*g^2 is the g.f. of A000108.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =45a(6) =141a(7) =457a(8) =1521a(9) =5164a(10) =17817a(11) =62293a(12) =220222a(13) =785898a(14) =2827341a(15) =10243147a(16) =37338298a(17) =136845402a(18) =503965327a(19) =1864003768a(20) =6921212392a(21) =25789735687a(22) =96405693388a(23) =361434199571